1. Field
This invention relates to bearing support systems for rotating archery bow elements. It is particularly directed to bearing support systems for use with rotating compound bow eccentric pulley members.
2. State of the Art
Compound archery bows commonly carry pulley members concentrically or eccentrically mounted on axles in association with respective bow limbs. These limbs extend in opposite directions from a grip (usually comprising a central portion of a handle riser). The rigging for compound bows includes a bow string trained around the pulley members of the system, the string being received by grooves or other features at the perimeters of the pulleys. Certain pulley members are conventionally mounted to rotate (pivot) on an axle within a notch at the distal end of the limb, or within a bracket structure carried by the limb tip. An additional leverage advantage may be provided by specialized pulleys, usually called xe2x80x9ceccentricsxe2x80x9d or xe2x80x9ccamsxe2x80x9d. Some bows are constructed with grooved idler wheels, or pulleys, at the limb tips, and carry the eccentric of the system on the handle riser or at some intermediate position on the bow limb. Other bows are constructed with an idler wheel mounted at one limb tip and a cam at the opposite limb tip. In any case, the eccentrics include a pivot hole which is substantially offset from center, whereby to provide for a reduction in the holding force felt at the nocking point of the bow string, as the string is moved to its fully drawn condition. This location of the pivot hole inherently positions the axle closely adjacent the perimeter of the eccentric, in some cases within a quarter of an inch of the cable track. Such close spacing doesn""t allow room for a bearing system other than a simple sleeve bearing or bushing. Accordingly, it has become conventional practice to journal the pivot axle of an eccentric through a sleeve bearing mounted within the pivot hole of the eccentric. While bows have functioned well with this system, sleeve bearings inherently limit the wear life, accuracy and stability achievable with compound bow eccentric systems. Sleeve bearings or bushings also inherently possess increased friction compared to other, more desirable, bearing assemblies.
This invention provides a bearing system for rotating archery components, used in compound archery bows, which differs significantly from the simple journal bearings currently ubiquitous in the art. The utilization of a bearing system characterized by very low friction, as compared to sleeve bearings, constitutes a significant advance in the art. Moreover, the system of this invention provides for a wide stance between bearing surfaces at opposite sides of the pulley. Bearings which provide a rolling frictional interface for the pivot axle of the pulleys in the rigging of a compound bow are now practical, by virtue of this invention.
The present invention reduces rotational friction and enhances lateral stability of the supported rotating components. The system of this invention provides enhanced lateral stability of the rotating components typically by providing stable component mounting on paired, axially spaced apart, bearing elements. With this invention, it is now possible to mount eccentrics to a bow using rolling bearing supports, such as ball bearing assemblies. Other types of bearing elements may also advantageously be used with the present invention to reduce pulley wobble and decrease rotational friction. The present invention allows use of low cost, commercially available, ball bearing elements having a diameter too large to mount within certain rotating archery components, such as cam elements typically disposed at limb tips.
One embodiment according to this invention includes a first support structure configured to receive a first bearing, the first support structure being adapted to rotate with the pulley and arranged such that the first bearing is mounted substantially outside of the body of the pulley, or outside the body of a let-off cam component of a multicam eccentric. Certain exemplary embodiments of the invention also will have a second support structure adapted to rotate with the pulley and arranged to receive a second bearing mounted substantially outside of the body of the pulley. The first and second bearing assemblies may be characterized as providing rolling friction, and are typified by self-contained ball bearing assemblies. Bearing support structure may be fashioned as one or more modular support elements configured for a press-fit or other engagement within receiving structure of the pulley. The bearings typically are axially spaced apart by a distance corresponding approximately to the width of a working surface of a cam forming the pulley. The axial spacing provides a moment arm, to resist a pulley tipping moment and pulley wobble, having a length typically greater than a length given by of the sum of the width of the pulley body and a rotational clearance. The moment arm to resist pulley wobble may be greater than one-and-a-quarter times the width of the pulley body.
The invention can be embodied in a compound bow eccentric assembly of the type that mounts a pulley body to a limb by means of a pivot axle extending through a bearing arrangement. Such an embodiment may include a first bearing assembly constructed and arranged to provide a rolling friction interface for a pivot axle. The first bearing assembly generally includes a first bearing support configured to rotate with the body and to support a first rolling bearing element substantially outside of the body. Another embodiment might further include a second bearing assembly constructed and arranged to provide a rolling friction interface for the axle. The second bearing assembly can include a second bearing support configured to rotate with the body and to support a second rolling bearing element substantially outside of the body. The first and second bearing supports may be modular components structured to interface with structure carried by the body. Alternatively, the first and second bearing supports may be axially directed extensions from material forming the body. In any event, it is currently preferred for the bearings to be ball bearing assemblies.
The instant invention can function to mount a pulley body to a bow limb by means of a pivot axle extending through a bearing arrangement including a bearing assembly having a first bearing support which rotates with the body. The bearing assembly typically provides spaced apart supports for the axle at opposite sides of the pulley body. At least one such axle support is generally located on an opposite side of a plane from the body. A second bearing support which rotates with the body may further be included. First and second bearing supports may alternatively be affixed to a bow limb or riser. The bearing supports typically carry bearings to provide axle supports spaced apart by a distance. In any case, the instant invention provides a moment arm, substantially greater than the width of a working surface of a cam forming the pulley, functioning to resist wobble of the pulley. The space between individual bearings may be more than xe2x85x9 inch. It is within contemplation also to use a single, extra long, bushing in combination with the axle bearing support structure of the instant apparatus. The axle supports may be described as providing a moment arm to resist a wobble moment, with the moment arm having a length greater than about one-and-a-quarter times the width of the pulley body.
The invention generally provides bearing support structure configured and arranged to secure first and second bearing elements spaced apart by a distance along a pivot axle whereby to provide increased stability of a pulley from wobble during pulley rotation. Bearing elements providing a rolling bearing interface between the pivot axle and the bearing support structure may be used. Preferred bearing elements include roller and ball bearing assemblies. Bushing elements are also workable. In any case, it is currently preferred to have a race element disposed between the pivot axle and the elements providing the rolling interface. Such a race element prevents premature wear of the axle. The bearing assemblies are typically secured in the support structure such that the bearing assemblies are spaced apart by a distance substantially on the order of a width of the pulley body. The bearing support structure, in certain preferred embodiments, may be fashioned as a hanger bracket affixed to a limb, a limb tip overlay affixed to a limb, a built-up area in a limb, or as a portion of a limb tip constructed to receive either the bearing assembly or a pivot axle.
These features, advantages, and alternative aspects of the present invention will be apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings.